github: add bug report and pull request template

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,42 @@
+---
+name: Bug report
+about: General issue
+title: ""
+labels: bug
+assignees: stevearc
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**System information**
+
+- OS: [windows/linux/mac]
+- Neovim version:
+- Is this related to a specific `vim.ui.select` backend? If so, which one?
+- Dressing config:
+
+```lua
+-- Paste your call to require("dressing").setup(...) in here
+```
+
+**To Reproduce**
+Steps to reproduce the behavior:
+
+1.
+2.
+3.
+
+If possible, provide a minimal file that will trigger the issue (see
+[tests/manual](https://github.com/stevearc/dressing.nvim/tree/master/tests/manual)
+for examples of short ways to call `vim.ui.*`):
+
+```
+minimal code here
+```
+
+**Screenshots**
+If applicable, add screenshots to help explain your problem.
+
+**Additional context**
+Add any other context about the problem here.

.github/PULL_REQUEST_TEMPLATE.md

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+_2 sentence summary of change_
+
+## Context
+
+_What is the problem you are trying to solve?_
+
+_If related to an issue, please link it here. You may omit some background
+details if it is in the issue._
+
+## Description
+
+_Describe how the changes add the functionality or fix the issue under "Context"_
+
+## Test Plan
+
+_list the steps you took to test this functionality. Steps should be
+reproducible by others._